A small rock is thrown straight up with initial speed V0 from the edge of the roof of a building with height H. The rock travels upward
and then downward to the ground at the base of the building. Let
+y be upward, and neglect air resistance. (a) For the rock’s motion from
the roof to the ground, what is the vertical component Vav-y of its average
velocity? Is this quantity positive or negative? Explain. (b) What
does your expression for Vav-y give in the limit that H is zero? Explain.
(c) Show that your result in part (a) agrees with Eq. (2.10).

Hugh D. Young, Roger A. Freedman - University Physics with Modern Physics (15th Edition) Chap. 3 Ex. 73